Proper 3D box without being resized?

Hello,

I have to make a rotating prism for banners. My problem is the following:
If I add ‘perspective: 1000px’, the box gets resized, which is bad because the picture in box also would also get resized.
If I don’t add perspective, the size of the box is okay, but the rotation is not realistic, because while rotating, the left and right sides of the box remain parallel/vertical.

Here you can see the two results:

1. with perspective
2. without perspective

• You can rotate the box with keys up and down.
• There are some vertical lines in side ‘1’. If they’re wavy, it's because the box is resized.

Is there a way to make the prism rotate like in the ‘with perspective’ version, but without resizing it?

Thanks!